function add (x,y){
    // return Math.pow(x,y)
    if(typeof x == 'number' && typeof y == 'number'){
         return x + y;
    }else{
        return Number (x) + Number (y);//显式类型转
    }
 
}


console.log(add('1',2));                                                                                                                                                                                      
